Falling film evaporator



oct. 9, 1951 Filed Sept. 9, 1946 J. A. cRoss 2,570,211

FALLING FILM EVAPORATOR 4 Sheets-Sheet l 7, f Egg OC. 9, 1 A CRQSS FALLING FILM EVAPORATOR Filed Sept. 9, 1946 4 Sheets-Sheet 2 Oct. 9, 1951 J'. A. cRoss FALLING FILM EVAPORATOR 4 Sheets-Sheet 3 Filed Sept. 9, 1946 FIJ Oct. 9, J, A, CROSS FALLING FILM EVAPORATOR Filed Sept. 9, 1946 4 Sheets-Sheet 4 Patented Oct. 9, 1951 FAI-LING FILM EVAPORATOB Joseph A. Cron, Westerville, Ohio, assigner to Moionnier Bros. Co., Inc.,

poration o! Illinois Chicago, lll., a cor- Application September 9, 1946, Serial No. 695,641

4 C lalms. (Cl. 159-13) 'I'his invention relates to evaporators and particularly to those designed for continuous rather than batch operations.

A feature of the invention resides in the provision of multi-stage evaporation, not according to the usual multiple effect wherein the hot vapors of one stage heat the liquor in the next, but rather by maintaining segregated bodies of liquor of different densities heated' from a common heat supply source and connected to a common vapor exhaust.

While the apparatus is suitable for evaporation at various pressures and temperature levels. it oil'ers especial advantages at the low temperatures obtainable under vacuum.

One of theobiects of the invention is to provide evaporation apparatus suitable for continuous operation and using tubular evaporators of the falling illm type.

Another object of the invention is to provide a multi-stage evaporator system in which the liquor progresses through connected bodies of the liquor maintained at different densities and subjected to evaporation by heat supplied from a common source of condensible vapor.

Other objects and advantages of the invention will be apparent from a. perusal of the following speciilcation wherein a preferred and a modifled embodiment of the invention are described.

On the drawings:`

Figure 1 is a side elevation of an evaporator made in accordance with this invention;

Figure 2 is a top plan view of the same evaporator;

Figure 3 is a sectional view on the line III-III of Figure 1;

Figure lfis an end view of the evaporator;

Figure 5 is a partial sectional view of one of the elements of the evaporator taken on the plane L of line V-V of Figure 1;

Figure 6 is a partial sectional view taken on the plane of line VI-VI of Figure 4;

Figure 7 is a side elevation of a modified form of the evaporator units; and e Figure 8 is a sectional view on line VIII-VIII, of Fig. 7 with the lower portion of one evaporator also in section.

Figure 9 is a horizontal sectional view on the line IX--IX of Fig. '1.

Referring first to Figs. 1 to 6 of the drawings, the evaporator is comprised of an assembly of substantially identical units interconnected in order to afford a system of multi-stage evaporation. Each unit includes a vertical tube chest such as the chest I. Each tube chest contains a plurality of tubes such as 2 held in the upper and lower tube sheets indicated as 3 and l, in Figures 5 and 3, respectively. The upper ends of the tubes open into a chamber 5 at the top of each tube chest, into which the liquor to be evaporated is introduced by means of a pipe 6.

As stated before, the evaporator units are of the falling iilm type. Accordingly, in order to feed the liquor into the evaporator tubes in the form of iilms I provide a. removable tube 'l inserted into the top end of each evaporator tube 2, and supported by spiders 8 which may be welded or otherwise secured to their outer surfaces, the three or more legs of the spiders resting upon the upper tube sheet 3. The lower end of each tube 1 is flared out at 9 to restrict and deilect the downwardly flowing liquor against the tube walls. The rate of flow of liquor into the tubes 2 of each evaporator may be varied by increasing the depth of the body of liquor maintained above the upper tube sheet 3, by regulating the rate of delivery of liquor through the pipes i into the chambers 5. The static head thus will determine the rate of iiow of the nlm and may be controlled to assure the maintenance of a lm in each tube to its bottom end. Of course, overiiowing the top of the tubes l is to be avoided. The top of each chamber 5 will be closed by a cap III.

The heating medium, such as steam, a refrigerant gas, or other condensible vapor is preferably introduced into the upper portion of each tube chest from a common supply pipe II connected with an individual supply pipe I2 leading to each tube chest. The condensate which may be drained from the space around the tubes at the bottom of each tube chest may be withdrawn from each tube chest through a pipe I! into a. common pipe I 4.

Directing attention now to the construction at the lower end of each tube chest, it will be noted that a generally cylindrical device is associated with each of the tube chests at their lower ends.

.These devices are a series of drums I5 having abutting inwardly extending flanges I 6 which preferably will be welded together. These flanges do not extend across the entire diameter of each drum but instead are apertured at Il thus providing a. common passage "through which vapors from the evaporating liquor mayl be withdrawn rapidly from the respective drums and tube chests to a common duct or pipe I8. At the bottom end of each tube chest is a curved hood I9 which opens into the adjoining drum vapors `and prevent their more direct escape through the ports` II. Thus, the vapors being extracted from the falling film of liquor are deflected in a circular path from the lower open ends of the tubes into the related drums I5, while any unvaporized liquor is allowed to fall through the hood I9 into the sump 20.

As indicated, there is connected with the bottom of each sump a pipe 2l leading to a pump 22, each pump being preferably driven by an electric motor and delivering its output to a riser pipe 6, which as noted before delivers the liquor into the chamber at the top of each tube chest.

The fresh dilute liquor to be evaporated will be introduced through a pipe 23 into the downiiow pipe 2I of the first evaporator unit where it will be drawn through the pump 22 and thence delivered upwardly through the riser pipe 6 into the top of the first evaporator chamber 5. It is contemplated that some of the liquor will recirculate through the rst evaporator unit many times as the vapor is being extracted from it in the falling nlm tubes.

A draw-oir pump 24 connected with the drawoi pipe 25 maintains a continuous discharge of concentrated liquor from the last evaporator. Between the rst and second units, that is, connected with their sumps, is a pipe 26 and between the sump of the second unit and the sump of the third unit is another pipe 21. The operation of the draw-oil` pump and the feed of fresh liquor through the pipe 23 will therefore induce a continuous ow of liquor from the rst unit to the second and from the second to the third and from the third to the draw-oil pump or to such other units as may be connected between that point and the draw-off pump.

While three connected units are shown in the evaporator herein described, it is contemplated that as many as are necessary for high output and eiiiciency oi' operation will be employed. In view of the fact that the units are identical in construction, the cost of manufacture and assembly is thereby simolied. Also, the use of identical units simplies the determination of ideal operating conditions and facilitates the determination, by experiment or by calculation, oi' the number of units required for the most efcient operation on any proposed installation.

The operation of the device, brieiiy, is as follows:

Fresh liquor is supplied through a pipe 23 to the down-flow pipe leading to the pump connected with the rst unit. 'I'his liquor along with other liquor already in the system is delivered to the top of the iirst unit and under the controlling eii'ect of the static head and the tubes 1 will cause a iilm of the liquor to vflow downwardly along the entire inside of each of the 4 of the drum and rali back into the sump of each drum while the vapor, free from droplets, may be evacuated through the vapor outlet pipe I6.

The rate ofevaporation will be highest in the rst unit and lowest in the last evaporator unit. As a result the second unit will be operating on a liquor of considerably higher density than the fresh liquor introduced into the first unit. The liquor flowing from the second unit to the third unit will have an even higher density, and during its recirculation and subjection to evaporation in the third unit may be caused to attain the iinal desired density. The rate of withdrawal of liquor through the draw-ofi pipe 25 will be maintained at such a rate as to make certain that liquor of the desired density only is withdrawn.

It is clear that a large numberv or a small number of identical units may be connected in series, as described, in order to obtain a desired concentration under eiiicient operating conditions.

As stated hereinbefore, the present invention is especially suitable for evaporation of liquors at low temperatures such as are made possible by evaporation under vacuum. In such case, suitable equipment is connected with the vapor outlet pipe I8, that is, such as pumps or condensers or both, to maintain as high a degree oi' vacuum in the vapor space within the drums and within the tubes as may be desired.

Obviously, the means for evacuating the vapors will be suited to whatever vapor pressures, positive or vacuum, prevail in the system. Variable speed pumpsfvalves, or other devices may be employed for maintaining uniform or providing variable operating conditions.

In Figures 7 and 8 I`have shown a modified form of the evaporator units, the modication consisting in a diierent vapor separation device at the bottom of each evaporator unit, to cause the vapors to rotate about a vertical axis, instead of a horizontal axis as in the units heretofore described.

In this modiiication I have shown three vertical tube chests 30, the upper ends of which will be constructed as are the tube chests in Figures 1 and 5, being provided with insertable tubes in their upper ends for producing a iilm ow and assistingr in regulating the rate of iiow. The lower ends of the tubes, however, do not open directly into the vapor separator drum or hood as do the tube chests shown in Figure 3. Instead, the vapors and unvaporized liquor emerge from the lower ends oi' the vertical tubes, through lower tube plates 3i and fall into the chambers 32 and then iiow outwardly through the'horizontal ducts 33 and enter tangentially into the associated vertical separator cylinders 34. The unvaporized liquid, being thrown centrifugally against the walls of the cylinders 34 by the i'orce of the rapidly iiowing vapors falls downwardly into the sumps 35 and will be recirculated back again through each unit through the pipe 36, recirculating pump 31 and the riser pipe 38, entering the liquid chamber at the top of the unit.

'I'he vapors thus separated from the liquor in the cylinders 3l will be evacuated upwardly into the horizontally extending drum 39. It will be noted that the units consisting of the tube chest, vapor separator, and recirculation pipes and pump are identical. Vapor from all of the separators may be withdrawn from the horizontal asmanf drum. by the action of a plunp, or condenser or other suitable means for evacuating these vapors, through outlet lll.

A difference will be noted between the drum Il and the series of connected-drums, l shown in Figure 1. which assist in the centrifugal separation of the vapor and droplets. No such flanges are required in the device shown in Figmes 7 and 8.

When employing the apparatus shown in Figures 7 and 8 the fresh liquor to be evaporated is introduced through a pipe Il into the downilow pipe 36 of the ilrst unit at the right of Figure 7 and is evaporated and reclrculated rapidly through the first separator unit according to the same principles applied in the other form of the invention heretofore described. There will be a constant ilow of partially concentrated liquor from the sump of the first unit through a pipe 42 into the sump of the second unit and the constant flow of further concentrated liquor from the sump of the second unit through a pipe 43 into the sump of the third unit. From the sump of the last unit the liquor concentrated to a predetermined density will be withdrawn through a pipe I4 by means of the pump I5, which, if desired, may have a variable speed to permit control in the rate of withdrawal.

Heating medium, such as steam, refrigerant gas or other condensible vapor, is preferably introduced into the space surrounding the tubes in chests 3u of Figs. 7 and 8 by means o f a common supply pipe li and individualinlet pipes such as Il, while the condensate from the heating medium may be withdrawn from the bottom of such space through individual outlets Il connected to a common outlet duct 49.

While I have shown and described herein, for

1. An evaporator comprising a series of vertical tube chests each having vertical tubes and top and bottom plates retaining the imbes, means for supplying heating fluid from a common supply source simultaneously to the space surrounding the tubes in eachV chest, heating fluid exhaust means connected with each tube chest, top and bottom chambers in each tube chest with which the tubes communicate, removable open ended film feed control tubes resting on the top plates extending downwardly a short distance only into the upper ends of the tubes and rising above the top tube plates, an enlarged vapor separator associated with each chest for extending the vapors received from the lower ends of the tubes and for separating liquid droplets therefrom, the top chamber having an outlet for vapor only through said control and chest tubes, means connected for delivering vapor and droplets from each bottom chamber tangentially into the associated separator for centrifugal flow about a vertical axis in the separator, means connected with the lower portion of each separator including a pump for returning liquid therefrom to the top chamber of the associated tube chest for return flow through said vertical tubes, vapor outlet means connected with the upper portion of each separator, pipes connecting the bottom portions of each separator with the next adjacent separators to effect liquid ilow in one direction from These latter drums have flanges 6 the ilrst successively through to the last in the series of separators, means for supplying to the first tube chest-evaporator unit liquid to be evaporatedand means for withdrawing from the last in the series of tube chest-evaporator umts the concentrated liquid. v

2. An evaporator comprising a series of vertical tube chests each having vertical tubes and top and bottom plates retaining the tubes, means for supplying heating fluid to the space surrounding the tubes in each chest, heating fluid exhaust means connected with each tube chest, top and bottom chambers in each tube chest with which. the tubes communicate, removable open ended film feed control tubes resting on the top plates extending downwardly a short distance only into the upper ends of the tubes and rising above the top tube plates, an enlarged vapor separator associated with each chest for expanding the vapors received from the lower ends of the tubes and for separating liquid droplets therefrom, the top chamber having an outlet for vapor only through said control and chest tubes, means connected for delivering vapor and droplets from each bottom chamber tangentially into the associated separator for centrifugal ow about a vertical axis in the separator, means connected with the lower portion of each separator including a pump for returning liquid therefrom to the top chamber of the associated tube chest for return flow through said vertical tubes, vapor outlet means connected with the upper portion of each separator, pipes connecting the bottom portions of each separator with the next adjacent separators to eifect liquid ilow in one direction from the rst successively through to the last inthe series of separators, means for supplying to the rst tube chest-evaporator unit liquid to be evaporated and means for withdrawing from the last in the series of tube chest-evaporator units th concentrated liquid.

3. An evaporator comprising a series of vertical tube chests each having vertical tubes and top and bottom plates retaining the tubes, means for supplying heating fluid to the space surrounding the tubes in each chest, heating fluid exhaust means connected with each tube chest. top and bottom chambers in each tube chest with which the tubes communicate, removable open ended film feed control tubes resting on the top plates extending downwardly a. short distance only into the upper ends of the tubes and rising above the top tube plates. an enlarged vapor separator associated with each chest for expanding the vapors received from the lower ends of the tubes and for separating liquid droplets therefrom, the top chamber having an outlet for vapor only through said control and chest tubes, means connected for delivering vapor and droplets from each bottom chamber into the associated separator, means connected with the lower portion of each separator including a pump for returning liquid therefrom to the top chamber of the associated tube chest for return flow through said vertical tubes, vapor outlet means connected with the upper portion of each separator, pipes connecting the bottom portions of each separator with the next adjacent separators to effect liquid ilow in one direction from the first successively through to the last in the series of separators, means for supplying to the rst tube chest-evaporator unit liquid to be evaporated and means for withdrawing from the last in the series of tube chestevaporator units the concentrated liquid.

4, An evaporator comprising a series of verthe tubes vin each chest, heating fluid exhaust means connected with each tube chest, top and bottom chambers in each tube chest with which the tubes communicate, removable open ended illm feed control tubes resting on the top plates extending downwardly a short distance only into the upper ends ofthe tubes and rising above the top tube plates, an enlarged vapor separator associated with each chest for expanding the vapors received from the lower ends of the tubes and for Aseparating liquid droplets therefrom, the top chamber'having an outlet for vapor only through said control and chest tubes, means connected for deliveringvapor and droplets from each bottom chamber tangentially into the associated separator for centrifugal ilow about a vertical axis in the separator, means connected with the lower portion of each separator including a pump for returning liquid therefrom to the top chamber of the associated tube chest for return ilow through said vertical tubes, a common vapor withdrawal duct mounted upon and in unrestricted communication with the upper ends of all of the vapor separators, pipes connecting the bottom portions of each separator with the next adjacent separators to effect liquid flow in one direction from the rst successively through to the last in the series of separators, means for supplying to the first tube chest-evaporator unit liquid to be evaporated and means for withdrawing from the last ln the series of tube chest-evaporator units the concentrated liquid.

JOSEPH A. CROSS.

REFERENCES CITED The following references are of record in the rile of this patent:v

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